French Pat. No. 1 534 907 of June 22, 1967 describes an activatable electrochemical battery comprising a stack of flat elements connected electrically in series, with each flat element being constituted by a plurality of elementary cells which are electrically connected in parallel. The electrodes of each cell are provided with connection lugs situated at the periphery of the stack. Same-polarity lugs of the electrodes are interconnected by metal spacers and constitute a terminal for the corresponding element.
The flat elements are stacked on one another by threading their output terminals on two rods. Electrical series connection is obtained by successively threading a positive terminal and then a negative terminal and interposing a metal spacer or an insulating spacer as appropriate.
It has been observed that the above structure gives rise to leakage currents which are excessive. French Pat. No. 2 539 917 proposes limiting these leakage currents by providing perforations in the electrodes themselves for the purpose of threading on the connection rods, rather than providing perforations in peripheral external lugs. This disposition is still insufficient for activatable batteries using lithium/thionyl chloride or lithium/sulfuryl chloride.
The problem posed by using such batteries is very acute since they must be capable of satisfying the following two requirements:
open-circuit standby after activation for a period of several hours, which means that leakage currents must be completely eliminated; since in addition to the loss of capacity to which they give rise, leakage currents also set up a secondary phenomenon in which lithium foam is deposited, which foam may give rise to short circuits; and
high rate discharge over a few minutes, thereby generating a large amount of heat.
It is therefore necessary to simultaneously solve a problem of electric insulation and a problem of controlling the temperature rise of the battery since an excessive temperature rise could lead to an explosion.
The object of the present invention is to solve this combined problem.